Q: What would Earth be like if it didn’t turn?

Physicist: The side of the Earth facing the sun would quickly become hotter than boiling water, and the side facing away would be cold enough for the atmosphere to freeze solid (condense into nitrogen and oxygen ice). So all of the air and water would form glaciers of ice and what-was-once-air on the night side of the planet, and the day side of the planet would become an airless desert. Without air to scatter sunlight, the sky would always be black, and the stars always visible.

Here I’m assuming that the Earth, rather than not rotating at all (which would result in one-year-long days), is in “phase lock” with the Sun the same way the Moon is in phase lock with the Earth. So one side would always face the Sun and the other would always face away.

Air and water on the dark side of the earth would freeze. The Earth would be half desert, half water/air glaciers, and all atmosphere free.

We can estimate how hot and cold things would get by considering the Moon. It’s the same distance from the Sun as the Earth is, so it’s a good test case. Very quickly (within a few minutes) after the Sun rises at the beginning of the Moon’s 709 hour day the surface gets about as hot as it’s going to get: a balmy 110°C/230°F (give or take).

Some craters on the moon are never exposed to sunlight at all, which is exactly the situation the dark side of the Earth would be in, writ small. They get as cold as -240°C/-400°F (that 30°C above absolute zero!). That’s cold enough to freeze oxygen and nitrogen solid, even without air pressure. So on the day side everything would get roasted, the oceans would evaporate out of their basins, and then drift to the dark side where they would form and condense onto massive glaciers.

For water at least, this is an effect already at work on our Earth (“spin Earth”?, “Rotopolis”?), it just doesn’t get very far. That’s why (for example) the Antarctic ice cap is on average about as thick as the ocean is deep!

The non-rotating planet is a staple of sci-fi, and generally it’s declared that life could survive in the “twilight ring” between the day and night sides. In fact, in the twilight ring the temperature would be colder than our poles are today (which are kinda like “twilight points”). You find the “comfortable zone” about 20° into the day side from the ring.

Not that it matters. What with the atmosphere being in such a state that you’d need a hammer and chisel to breathe, it wouldn’t be possible for life to exist anywhere. The set up we have now is pretty good by comparison!

18 Responses to Q: What would Earth be like if it didn’t turn?

So, a related question: suppose Earth was in the above state: phase lock with the Sun, no life at all, a desert hemisphere and another full of frozen air. Then an advanced alien species finds it and decides it’s a perfect candidate for terraforming, what with all the available water and such, with the added benefit that it’d “just” require making it spin once every 24 hours or so for things to settle into a nice pattern after a while.

What would be energy requirements of something like this? How could it be done (I’m guessing that gluing rockets to the ground and to the top of mountains wouldn’t work)? How much time would it take? And once the Earth was spinning, how long would our hypothetical aliens have to wait to be able to start colonizing it (think the frozen air and ice melting into an atmosphere and ocean, plus a climate regime, similar to ours)?

The Earth has about Joules of energy tied up in its rotation right now (about tons of TNT), which is just stupid-alot. It’s hard to say how long it would take. Suppose it depends on how motivated the aliens are?
I couldn’t even give a ball park guess for how long it would take for all the ice that’s supposed to melt, to melt. I once made a really big snowman that didn’t melt completely until July. So… tens of thousands of years? We really need to get some kind of resident climatologist.

Can the 2.5 x 10^29th power Joules of energy be generated with something like the theoretical moon forming event? You know, a huge asteroid slamming into the earth?

Which also brings up my next batch of questions:
i) Does the moon’s existence or non-existence affect the resultant rotation? Would having a moon help with starting the rotation, or as the current situation, slowly slowing the earth’s rotation?
ii) What are the chances of the planet-slamming event creating a moon/second moon? Other possible outcomes? (like a ring around the earth, for example)

The thing that hit the Earth and formed the moon (according to the most recent simulations) was about the size of Mars (it’s been posthumously named “Theia“), and that should be enough to get the Earth spinning again. However, it would also liquify the surface. But, if that’s not a problem, then slamming the Earth with something gargantuan should do the trick.
The moon’s orbit is related to the rotation of the Earth. Since the moon’s formation it’s been slowly leaching away angular momentum from the Earth, making our days longer and the moon’s orbit higher (it started out about 15 times closer).
If the Earth were not spinning, the moon would very, very slowly start Earth’s rotation back up again, until the Earth and moon were both in phase lock (same sides always facing each other).
I don’t know what fraction of the simulations end with a new moon being created, however I’d wildly guess that the presence of our present moon might actually screw up the formation of a new moon. Small ring system; for a while, probably.

The atmosphere would stop this from happening.
Example EARTH.
The poles have MONTHS of constant night at a time and this scenario doesn’t happen! The record cold is -89c/194k
If the planet was very watery, then the parts with constant strong sunlight would have large amounts of water evaporating, the water would then be replaced by water currents from colder places, this woauld keep the maximum temperature at something where evaporation is quite rapid, 70c-90c maybe? The evaporating water would travel to darker areas and then rain down, so there would be a lot of cloud cover. This would likely help spread the heat. Overall the bigger the atmosphere the better it would be.

I’m commenting really late, hope this doesn’t get lost in history:
Quite unlikely Mr. Physicist. Considering the radiation intensity of Sun at Earth’s orbit, 1366W/m^2, black body temperature is about 394K. Well above the boiling point of water, but Earth is not a black body, and the atmosphere is rather indifferent towards this temperature. What make planet Earth temperate are the convective and high specific heat capacity fluids, and rotation. Now you just take one away. Convection will be working alone, but will be stronger too. And let’s not forget about the “heat wave” that forms traveling through the ground when stoppage happens, although it might take thousands of years to get to the other side, but it will, and affect.
To sum it up, Earth is more likely to become Venus like, not Mars like.
Cheers
Mehrdad from Tehran

A planet that never turns will not be tidally locked to its star. Since it doesn’t rotate at all, all sided of the planet will be in the dark for part of its resolution around its sun and part will lit. And that will constantly change as the planet revolves around its sun, since it doesn’t turn at all. However, if a planet was tidally locked to its sun, it would rotate once for every revolution it makes around the star and thus one side always faces the sun, but that means the planet does rotate at least once per its year. Both ways it is possible that a planet could maybe support life, as it depends on the distance from its sun, the thickness of its atmosphere, the amount of greenhouse gasses in the atmosphere, and even the size of the planet and thus its magnetic field and how well it protects the planet from solar radiation. This will all factor in to whether any such planet could support any kind of life. Also, a planet that is tidally locked to its sun could possibly support like right along the line that marks the twilight zone, marginal zone with daylight on one side and darkness on the other with eternal night and ice and cold, while the daylight side has is hot, and bare and arid. Also it could be a very windy area as the daylight side would have hot rising air while the night side as rapidly sinking air and strong horizontal winds blowing between the permanent high and low pressure regions. However, because of this constant exchange cool air coming in from the dark sight will absorb moisture from all the frozen surface and carry to the sunlit side and drop it as rain, and the warmth circulating toward dark side will melt some of that ice and extend some of the warmth toward the night side, thus creating a rather large belt of a habitable zone around the planet at that terminal point between the day and night sides. And if intelligent life developed on such a planet, their technology could extend that habitable zone even wider and even they didn’t destroy themselves and survived long enough, these being could make most of the whole planet habitable in some way.

Maybe all the frozen water and gas building up on the dark side of the earth would increase its mass relative to the light side. The Sun’s gravity would therefore pull the dark side around, restarting the Earth’s rotation.